Digital logic, in the form of integrated circuits, has found wide spread use in virtually every type of electronic system. The interface function is a basic function of any electronic system; it allows the logic of one IC device to interface with other devices. One important component for this interface function is the output buffer which, when enabled, provides an output which is a function of data received from other logic circuitry of the IC.
FIG. 1 shows a related art CMOS output buffer 10 which provides an output signal at output line 18 based upon a DATA signal received at data input terminal 4 and an ENABLE signal received at enable input line 6. Output buffer 10 includes NAND gates 8 and 21, inverters 23, 25, 27, and 29, and a P-channel FET 14 and an N-channel FET 16. Power for all of the components of the output buffer 10 is provided by first and second power supply terminals Vcc (full voltage from the power supply) 15, and ground 17.
In operation, the main point to understand is that transistors 14 and 16 are large in order to provide enough current to communicate to other devices receiving output signals from the output buffer (or driver) 10 in response to the DATA input.